1. Field of the Invention
The present invention relates to a method for position determination as well as a position measuring device for executing the method.
2. Description of the Related Art
Incremental position measuring methods and position measuring devices are employed for the highly accurate measurement of the position of moved objects on machinery, such as machine tools or wafer steppers, for example. In the course of this, the position measuring device must measure the position of the object at strictly defined times, and the position must be supplied to the electronic control device which controls the movement of the object. The times are defined by the external electronic control device. So that a position value can be made available at these times, the position measuring device determines position measuring values in a predetermined time grid or on the basis of an external signal by interpolation of several scanning signals of the same frequency, which are offset with respect to each other.
In accordance with DE 27 29 697 A1, memory devices in the form of sample and holding circuits are arranged upstream of the interpolation unit, by which the instantaneous values of all scanning signals are simultaneously stored at the preset times. Position measuring values are formed in the interpolation unit from these instantaneous values. As expressly mentioned in DE 27 29 697 A1, this method is particularly suited to the measurement of moved objects.
It is disadvantageous here that the scanning signals in the individual scanning channels are affected by the signal generation—i.e. from the scanning location—up to the memory devices by different transit delays, which results in measurement errors in the interpolation.